1. Field of the Invention
The present invention relates generally to a method and a system for transporting natural gas between a natural gas pipeline and a compressed natural gas (CNG) station for the purpose of re-fueling automobiles, busses, and trucks, and other end-user uses. More particularily, it relates to such a method and system especially adapted to the economies involved with re-fueling stations that are remote from a pipeline where the cost of constructing a conventional pipeline extension to a re-fuel station site is excessive, (or extension is impractical due to regulations or other factors). These remote station sites must rely upon trucks and transport vessels to bring natural gas to the station site in steel tubes. The present invention relates, specifically, to the use of a flexible bladder to accept gas from the pipeline, hold the gas under pressure inside the outer steel transport vessel until the vessel reaches the station site, at which time the gas is un-loaded to storage by deflating the bladder. The deflation process will be accomplished by pumping a hydraulic fluid into the annulus between the bladder and the walls of the steel vessel. Without the presence of an internal flexible bladder, the vessel would have to be un-loaded with the assistance of an expensive compressor, which would increase the cost of delivery of natural gas to the re-fuel site and make it more difficult for natural gas to compete with gasoline and diesel as the primary fuel for autos, busses, and trucks.
2. Description of the Prior Art
The use of compressed natural gas (CNG) as fuel for automobiles, busses and trucks, has been known for many years, and is in use in many areas of the world. The conventional manner for handling the natural gas is to transport the gas, by truck-mounted high-pressure vessels, from a pipeline to re-fueling stations. While the system has proven successful, in many instances, the economic costs are so excessive as to make the use of natural gas non-competitive with conventional fuels such as gasoline and diesel.
In recent years, environmental-pollution concerns in many areas of the United States have focused attention on the use of alternative fuels, i.e., fuels for automobiles, busses, and trucks that emit less pollutants to the air than gasoline and diesel fuel currently in use. One of the least-polluting fuels is natural gas, which is being given a high priority by government and industry due to it's easy access and long term availability. The chief obstacle to a massive conversion from gasoline and diesel to compressed natural gas (CNG) is the cost to deliver CNG to a re-fueling station from the nearest natural gas pipeline. The industry is currently utilizing high-pressure tube-trailers (which were developed for other uses as described in U.S. Pat. Nos. 4,139,019, 4,213,476, and 4,380,242.) These tube-trailers are expensive to operate and have limited availability. One of the higher costs in using the high-pressure tube-trailers is that they must utilize an expensive compressor to un-load the gas when it arrives at the re-fueling station. It has also been demonstrated that natural gas can be liquified and stored in refrigerated vessels for transportation, as described in U.S. Pat. No. 3,232,725. The method requires refrigeration equipment and insulation to hold the gas in a sub-freezing temperature during transportation. The high cost of a liquification plant, in addition to the extra weight and space requirements under the method, makes it excessively expensive compared to the costs of gasoline and diesel, and much more excessively expensive as compared to compressed (not liquified) natural gas.
The present invention is intended to solve the need for economically transporting natural gas from remote pipelines to re-fueling stations. It is particularily designed to operate in a low-pressure (1000 psi) environment, compared to other equipment operating in a high-pressure environment (2400-3600 psi). Reduction of the system operating pressure to approximately 1000 psi will enable the transport vessel (with enclosed bladder) to accept gas at pipeline pressure, without additional compression, and transport the gas to a re-fueling station at approximately 1000 psi, where it can be off-loaded into storage by deflating the bladder with pressurized hydraulic fluid pumped into the annulus between the outside of the bladder and the inside walls of the steel transport vessel, which will deflate the bladder. Deflation of the bladder will force, or squeeze, the gas out of the bladder and into storage.
The present invention is particularily designed for economically transporting the natural gas over-the-road, and in this embodiment makes use of the general type of transport motor vehicles that have been developed for handling specialty gases (such as oxygen, acetylene, and natural gas) utilizing semi-trailers with a number of cylindrical high-pressure vessels. The modification of the method used to evacuate natural gas into storage, i.e., the deflating of the internal bladder with hydraulic fluid pressure, instead of using a multi-stage compressor which would be necessary in the absence of an internal bladder, reduces the total cost to move the gas from the pipeline to the re-fuel station, thereby making compressed natural gas (CNG) competitive with gasoline and diesel as the primary fuel for automobiles, busses, and trucks.
While the invention is primarily intended for transporting natural gas over-the-road, it can also be adapted for transportation by other means such as by barge, rail, or airplane. When these transport vehicles are employed, the elimination of the need for refrigeration equipment or high-pressure compression equipment will allow carrying a significantly heavier payload. It can also serve as a more economical method of transporting natural gas from isolated gas wells to a pipeline for sale, or, in some instances, for sale directly to a re-fueling station.